Evaluation of the vacuum infusion process objectives at the early stages of computer simulation

Increasing the quality and reliable reproducibility of large-size composite structures molding using the vacuum infusion method, which is gaining popularity in various industries, is achieved in practice through numerous tests by try and errors that require significant costs and time. The purpose of these tests is to determine the layout of the ports for the resin injection and vacuum supply, as well as the temperature regime that ensures the absence of isolated non-impregnated zones, the minimum porosity and the required reinforcement volume fraction in the composite. The proposed approach removes the simplifying assumptions used in commercial software for modeling the process, which reduce the accuracy of reconstruction of its dynamics and the sensitivity to the formation of unrepairable defects such as dry spots. It involves multiphysics modeling of resin filling in a porous preform by describing the resin front dynamics by the phase field equation, pressure distribution in an unsaturated porous medium by the Richards equation, the evolution of the degree of cure by the convection / diffusion / thermokinetics equation, and thermal processes by the heat transfer equation using modified models of viscosity, the diffusion coefficient of the degree of cure, the boundary condition for the vacuum port. To reduce the finite element computation time of the investigated variants of the process, which is necessary for its computer optimization, the predictive partial sub-criteria were used, which give a reliable prediction before the beginning of the resin gel and solidification. Due to this, a gain in computation time is 30-50% with a significant prediction accuracy of quality objectives and the presence of possible defects.

Mixed Finite Element Computation of Energy Release Rate in Anisotropic Materials Based on Virtual Crack Closure-Integral Method

The material with anisotropic properties are becoming widely essential due to the ease to manipulate their mechanical properties in order to obtain a particular quality, insure safety or a specific behavior. Those kind of materials are considered anisotropic because their characteristics and behavior are dependent to every direction of the material’s orientation. In this work, the virtual crack closure-integral technique is implemented to a mixed finite element, in addition with the stiffness derivative procedure, to evaluate the energy release rate of crack extension in anisotropic materials. A simulation of a cracked edge rectangular plat with anisotropic characteristics is taken for example. The results obtained are in good agreement with the analytical results, making the proposed technique a good model for fracture investigation and allow it to study more complicated cases in future works.

Finite Element Computation of Crown Deflection of Cracked Concrete Gravity Dam under Effect of Creep in Fracture Process Zone

The concrete dams contain micro-cracks and flaws, developed during the hardening of concrete. Under the influence of static and dynamic loads, tensile stress at the crack's end causes the crack to grow, leading to structural failure. In the present study, a Finite Element (FE) computation is present to account for an effect of creep and non-linear stress-strain behavior in the fracture process zone (FPZ) for analyzing the horizontal deflection of the crown of a dam. The model test was perform for an old existing concrete dam for deflection of the dam's crown for a single crack and the results were compare with field data. The present model successfully simulates the effects of non-linear stress and creep in FPZ on the horizontal dam-crown deflection. It concludes that the analysis of dam stability in conventional methods must include the stress field behavior in FPZ.

Effective thermal elastic plastic finite element computation for welding distortion investigation of pozidriv-type welded structure with rectangular pipes and its mitigation

Welding distortion of pozidriv-type welded structure with rectangular pipes by 20 welding passes was examined with experimental and computational approaches, and mitigation techniques were also investigated for precision fabrication. Welding experiment to fabricate pozidriv type welded structure was conducted beforehand, and out-of-plane welding distortion was measured with contact type displacement sensor. Effective thermal elastic plastic finite element computation with iterative substructure method and parallel computation was developed, and then employed to examine the thermal-mechanical response during the entire welding process and predict the residual out-of-plane welding distortion. Good agreement between computed results and measurement data was observed with comparison. The influences of welding sequence and clamping constraint with tack welding on welding distortion were considered, which were also practiced for out-of-plane welding distortion mitigation. Both experiment and finite element computation show that out-of-plane welding distortion with welding sequence optimization and clamping constraint can be significantly reduced with about 38% and 56% magnitude of original welding distortion, respectively, while their mechanisms were also clarified by means of stiffness variation of solving welded structure.

Thermal transient finite element computation of a mixing Tee by utilizing CFD results

Thermal distribution and fluctuation in any piping component due to turbulent mixing of flows with different temperatures vary greatly. Usually, computational fluid dynamics (CFD) tools are used for estimation of flows in piping components. Fatigue that results from fluctuating thermal mass flow across the components can be computed by coupling the CFD results with structural mechanics based finite element (FE) results. However, this procedure is laborious and computationally very expensive. A fluid temperature function has been developed in this paper as a function of internal wall coordinates and time by interpolating experimental or CFD results. Bicubic interpolation function has been used for accurate interpolation. Finally, a thermal transient FE analysis for an actual Tee from a nuclear power plant (NPP) was performed by using the developed fluid temperature function and interpolated CFD results.